Do you know what to do with it: what it can be used for, and how to use it?

If the answers are "yes", then you should carry one. If the answers are "no", then you should learn so that you can answer "yes".

However, a new jumper shouldn't go over-thinking malfunctions in order to try and find some way out of it with a hook knife. Stick to the basic emergency procedures. A hook knife is really only employed in very rare and highly unusual situations.